grandfather clock

[Keith] got his hands on a few grandfather clocks. Apparently the price tag is greatly reduced if you are able to get them second-hand. The mechanical timepieces require weekly winding, which is a good thing since you’ll also need to correct the time at least that often. But this drift got [Keith] thinking about improving the accuracy of these clocks. He figured out a high-tech way to adjust the timepiece while it’s ticking.

The first thing he needed was a source of super-accurate time. He could have used a temperature compensated RTC chip, but instead went the more traditional route of using the frequency of mains power as a reference. The next part of the puzzle is to figure out how to both monitor the grandfather clock and make small tweaks to its pendulum.

The answer is magnets. By adding a magnet to the bottom of the pendulum, and adjusting the proximity of a metal plate positioned below it, he can speed up or slow down the ticking. The addition of a hall effect sensor lets the Arduino measure the rate of each swing and calculate the accuracy compared to the high voltage frequency reference.

Just like the clock from Harry Potter, a team of media informatics students at the University of Munich built a grandfather clock that doesn’t keep track of time; instead, it keeps track of where everyone is, whether it be their university, work, or in prison.

The build uses Android and iOS apps on each team member’s cell phone to send their current location to a web server. A circuit built inside an old grandfather clock the team picked up from eBay communicates with the web server through a WiFly Shield to control a quartet of servos and drive the clock hands.

Because the grandfather clock only came with two clock hands, the team used a series of four concentric shafts to move each hand around the dial. With a bit of clever gear fabrication on their laser cutter, they were able to use unmodified servos move the hands all the way around the clock.

The avatars on the tip of each clock hand are the remains of decapitated LEGO minifigs, a choice that makes sense after viewing the build video available after the break.

[Vinnie] has a wonderful old clock from his grandmother; it’s an exquisite antique with a real mechanical movement and a charming set of bells that ring every hour. Unfortunately, those chimes are a bit of a disturbance to neighbors at 2 o’clock in the morning. Previously, [Vinnie] had been stopping the clock every evening, and hoped he would remember to start the pendulum in motion 12 hours later. This was a chore, so he decided to automate the process.

The build is simple and clever; a small stepper motor is mounted in the clock just underneath the pendulum. Every 12 hours, the stepper motor moves a lever and slowly stops the pendulum over the course of a dozen or so seconds, silencing the clock movement. Twelve hours later, the motor turns again setting the pendulum in motion.

The parts count for this build is very low – basically just an ATmega88, a Darlington array to drive the stepper, and a 32.768kHz crystal. We can think of a few friends and relatives with loud clocks in their house, so we might have to build a few of these to give away.

Take a look at the demo video after the break to see how [Vinnie] stops his grandmother’s clock every night.

Put a case around it and it would be a grandfather clock but for now it’s a pendulum clock made from LEGO pieces. The video after the break shows a great overview of the build. You can see the workings at several different angles, as well as a clip that has been sped up to show the movement of the weights over time. One weight, made from dead AA batteries, drives the clock and the other weight switches the winding motor. That motor acts to automatically wind the clock when the drive weight reaches the end of its rope.

This is a nice departure from the majority of clock projects we see as it utilizes mechanical concepts instead of electronic. Most of [Pmroskelly’s] build details are shared as comments on the Picasa album found at the link above. There are also some other videos such as the one showing how the escapement works.